Because of a number of factors, not the least important of which is the rising cost of gasoline, the development of automobiles which have engine components to accomplish efficient and economic use of gasoline fuel has become an urgent project of the world's technological community. Nor is there any indication that fuel costs will decline in the foreseeable future so as to reduce the importance of the development of inventions which effectuate more efficient combustion of the gasoline/air mixture fed into the engine cylinders.
In the four-stroke gasoline engine powering many automobiles, operation of the inlet and exhaust valves for each cylinder is coordinated with the position of the piston within the cylinder. During the first stroke of the piston, the induction stroke, the inlet valve is open so that an air/fuel mixture fed to the cylinder inlet from the carburetor via an intake manifold can be admitted into the cylinder. During the compression stroke the piston moves upwardly within the cylinder to compress the air/gas mixture. During this stroke, therefore, both the inlet and exhaust valves must be closed.
The third stroke, or power stroke, involves downward movement of the piston in response to combustion of the air/fuel mixture when it is ignited by a spark provided by a spark plug. Again, both valves must be closed in order to effectuate maximum downward force upon the piston. If one or both of the valves were open, the gases, while expanding, would, at least partially, be allowed to be vented through the open valve.
The exhaust stroke begins as the piston again begins upward movement within the cylinder. During this stroke, of course, the exhaust valve must be open so that the by-products of combustion can be vented therethrough. After venting of these by-products occurs, the exhaust valve closes and the inlet valve again opens in order to begin a new cycle.
Normally, the valves are biased to a closed position, and they are open according to a predetermined timing schedule. This timing is coordinated by a cam-push rod-rocker arm arrangement provided for each valve. As the cam rotates, it translates its rotary motion into axial motion of the push rod. The push rod, in turn, causes pivoting of the rocker arm to open the particular valve involved. Rotation of the cam is geared to rotation of a crank shaft common to all cylinders in the engine. The crank shaft is made to rotate by use of a connecting rod extending from the piston in each cylinder. Consequently, the up and down movement of the piston within the cylinder can be translated into appropriately timed opening and closing of the respective inlet and exhaust valves of the particular cylinder.
In some engines, the volume of the air/gasoline mixture introduced into the cylinders is dependent upon the speed of the engine and the particular mode of operation thereof. Specifically, if the engine is in a period of acceleration, the volume of gasoline being admitted to the cylinder will likely be greater than during a period of constant speed cruising, deceleration, or idling. If the cam profile has not been varied, the exhaust valve will open in accordance with the same timing schedule as it would during other modes of operation of the engine, and complete and efficient combustion of all of the air/gasoline mixture will not occur.
Technology has provided devices to cure this defect to some degree. Different methods have been invented to alter the cam profile so that the exhaust valve stays closed longer in order to effect more complete burning of the air and fuel. These devices are, however, mechanical means which delay the opening of the exhaust valve a fixed amount regardless of the speed and operational mode of the engine. Consequently, in certain modes of operation, complete and efficient combustion may have already occurred, and the exhaust valve has not yet opened. This also gives rise to less efficient operation of the engine.
Although valve opening and closing occurs at a high rate of speed, maximum engine efficiency is frequently not attained because of comparatively sluggish valve actuation. A high valve lift rate (that is, the speed of valve opening) can improve performance significantly over that obtained where valve lift rate is low.
It is to these problems in the art to which the invention of the present application is directed. It provides a structure which effectuates a delay in the opening of the exhaust valve so that the amount of delay is directly proportional to the engine speed. The delay is, in turn, directly proportional to the quantity of gasoline introduced into the cylinder. It, therefore, maximizes the efficiency of combustion regardless of the speed at which the engine operates and the richness of the air/fuel mixture.